The present invention relates generally to energy systems, and more particularly, to adaptive control of hybrid ultracapacitor-battery storage system for photovoltaic PV output smoothing.
With the high levels of penetrations of renewable energy resources in a power grid, e.g. Photovoltaic (PV), the system encounters challenges, e.g. power quality, voltage impact, etc. One of the concerns comes from the short-term high-frequency variances of the PV generation during unpredictable sudden weather changes, which has been reported at some central generation stations. A great effort has been put in the mitigation of the short-term fluctuation of PV power generation, which is generally referred to as smoothing or ramp-rate control. The perspective solution is to add proper energy storage buffer and active management system to mitigate the impact of short-term variances. The batteries, as the most common energy storage devices, have high energy density, but relatively low power density. Usually the PV power output smoothing requires frequent and high charging/discharging power from storage devices, which will greatly shorten the battery life.
In the literature, various control techniques have been recommended by researchers, for single-type or hybrid energy storage system. The power management system smooth out the PV power fluctuations through scheduling power generation or consumption among different energy storage devices. The power scheduling approaches include frequency-spectrum-based, constant-power-based, knowledge-based, rule-based, etc.
Accordingly, a hybrid energy storage system is needed to effectively utilize the characteristic of different storage devices, such as the ultracapacitor (UC), featured with high power density and relatively low energy density, and that can compensate for the battery system and alleviate the high power burden on battery system.